This paper presents a millimeter-wave bandpass filter (BPF) that has a narrow-band and miniature dimension. The proposed BPF employs a half-mode substrate integrated waveguide (HMSIW) topology to attain decreased dimensions. We etched compact spoof surface plasmon polaritons (SSPPs) structures onto two rhombus-shaped HMSIW cavities in order to obtain the ability to filter a narrow range of frequencies. In addition, two HMSIW cavities with rhombus-shaped configurations are connected in series to achieve a high selectivity. In order to obtain a transmission zero in high-frequency part, the microstrip line located at the center of the SSPP structure is enlarged and a metallic via is introduced. Numerical results demonstrate that, the center frequency of the proposed HMSIW-SSPP hybrid BPF is at 30.585 GHz, insertion loss is 2.2 dB, 3-dB bandwidth is as narrow as 3.2%, and the profile is 1.48λ × 0.51λ, which has strong potential for use in millimeter-wave communication and radar applications.